Add test plug for DateTime.now

src/util/DateTime.zig

@@ -67,7 +67,14 @@ pub fn parseRfc3339(str: []const u8) !DateTime {
     };
 }
 
+const is_test = @import("builtin").is_test;
+const test_utils = struct {
+    pub threadlocal var test_now_timestamp: i64 = 1356076800;
+};
+pub usingnamespace if (is_test) test_utils else struct {};
+
 pub fn now() DateTime {
+    if (comptime is_test) return .{ .seconds_since_epoch = test_utils.test_now_timestamp };
     return .{ .seconds_since_epoch = std.time.timestamp() };
 }